1. Field of the Invention
The present invention relates to a conductive paste and its usage and, more particularly, to a conductive paste and a method for production of multilayer ceramic capacitors employing the same as a material for internal electrodes of multilayer ceramic capacitors.
2. Description of the Prior Art
With recent miniaturization and densification of electronic equipment, considerable progress has made in miniaturization, enlargement in capacitance, and densification of multilayer ceramic capacitors. Such multilayer ceramic capacitors are generally produced by the steps of preparing ceramic green sheets with a dielectric ceramic composition, applying a conductive paste on respective green ceramic sheets by screen printing, stacking and bonding the green ceramic sheets by thermocompression, cutting the resultant multilayered body into green ceramic capacitor chips, firing the green chips to form capacitor chips with internal electrodes, and finally forming external electrodes connected to the internal electrodes on opposed sides of each of the capacitor chips to complete multilayer ceramic chip capacitors.
The conductive paste used in the above screen printing is generally composed of a metal powder, e.g., Pd with a particle size of 2 to 5 .mu.m, dispersed in an organic vehicle, the organic vehicle being composed of an organic binder such as ethyl cellulose or alkyd resin and a solvent therefor.
When producing the multilayer ceramic capacitors, it is required to apply the conductive paste to ceramic green sheets so that the resultant conductive layers have a dried thickness of 5 to 10 .mu.m. If the thickness of the dried conductive paste layers is less than 5 .mu.m, the internal electrode layers produced therefrom by firing are cracked and form a reticular structure, resulting in deterioration of electric characteristics such as capacitance and ESR. If the thickness of the dried conductive layers exceeds more than 10 .mu.m, it is difficult to improve the capacitance-volume ratio of the multilayer ceramic capacitors.
In order to meet demands for the miniaturization and densification of electronic equipment, it is required to make the dielectric layers thin as well as to increase the number of the internal electrode layers in the multilayer ceramic capacitors. However, the dried conductive paste layers of the prior art with a thickness of 5 to 10 .mu.m are too thick to produce multilayer ceramic capacitors with good reliability. Use of the conductive paste layers of the prior art can cause insufficient removal of the organic binder and large internal stresses in the green ceramic capacitor chips, resulting in occurrence of internal defects such as delamination.